An ODE Approach to the Existence of Positive Solutions for Semilinear Problems in R^N H. BerestyckiP. LionsL. Peletier Indiana University Mathematics Journal 1981 text pdf 10.1512/iumj.1981.30.30012 10.1512/iumj.1981.30.30012 en Indiana Univ. Math. J. 30 (1981) 141 - 157 state-of-the-art mathematics http://iumj.org/access/